Is VariableToStr your own function you wrote? Any reason why you're not using aqConvert.VarToStr?
In any case, the way that the driver works is that it uses whatever the top value is in the spreadsheet to determine how to read the rest of the values in that column. So, if param5 is an integer an integer in row 1 and a string in row 6, it's going to try and read it as an integer and may return it as a blank since NAN converted to string is blank.
Try explicitly formatting the values in your spreadsheet to the format you want. So, explicitly make the values integers, strings, etc.
